1. Field of the Invention
This invention relates generally to the field of subterranean drilling and material recovery. More specifically, this invention relates to the use of deep eutectic solvents and/or solutions to solubilize cellulose or modified cellulosic polymers used in subterranean drilling and fracturing operations.
2. Background of the Invention
Cellulose is one of the most abundant bio-renewable materials with a long and well-established technological base. Cellulose consists of poly-disperse linear glucose polymer chains which form extremely strong hydrogen-bonded supra-molecular structures making cellulose insoluble in water and most common organic liquids. Chemically-modified cellulose is significantly more soluble in water and imparts viscous properties to solutions making it useful as an ingredient in drilling and/or fracturing fluid useful in subterranean drilling operations. In the particular case of fracturing a formation, causing cracks to form in the subterranean strata, to allow for the production of hydrocarbon components with substantially greater ease, it is often necessary to clean the well bore and resulting fractures to remove cellulosic material that may have become deposited during the aforementioned operations and which will impede flow of hydrocarbons through the fractures and/or production.
As previously mentioned, cellulose is insoluble in water and most common organic solvents. Where chemically-modified cellulose is employed, it is not atypical for all or part of the material to be hydrolyzed under use conditions reforming the parent compound, cellulose, which will again become insoluble. Thus, given the frequency with which cellulosic material is employed in drilling and fracturing subterranean wells, the development of an additive and/or solvent for solubilizing cellulose and/or chemically-modified cellulosic material remains a continuing challenge in the oil and gas exploration industry.
In the prior art, room temperature ionic liquids (RTIL) can solubilize up to 15 wt % cellulose with heating to 150° F. employing preferably microwave heating. According to Swatlowski, et al. (U.S. Pat. No. 6,824,599), a solution of cellulose in an ionic liquid can contain cellulose in an amount of about 5 to about 35 weight percent; more preferably, the cellulose is present at about 5 to 25 weight percent, still more preferably from about 10 to about 25 weight percent. According to Swatlowski, this solubility of cellulose in (RTIL), such as [C4mim]Cl, is significantly higher than can be obtained using other solvents.
Consequently, there is a need for a method of removing cellulose and/or cellulosic compounds from a subterranean region. The method may prevent/minimize the deposition of cellulose and/or cellulosic compounds on or in the subterranean region or may solubilize deposited cellulose/cellulosic compounds deposited in a subterranean region, allowing removal thereof. Desirably, the method will allow better cost performance and/or improved toxicological and/or handling properties relative to RTILs, many of which react adversely with water.